domxml_new_doc() is not defined.

This is what you need to do:
From: http://www.php.net/manual/en/ref.domxml.php

Windows users will enable php_domxml.dll inside of php.ini in order to use these functions. In PHP 4 this DLL resides in the extensions/ directory within the PHP Windows binaries download. You may download this PECL extension DLL from the PHP Downloads page or at http://snaps.php.net/. Also, there is one additional DLL that must be made available to your system's PATH in order for this extension to work. In PHP 4 this is in the dlls/ directory. It's name: For PHP <= 4.2.0, it's libxml2.dll. For PHP >= 4.3.0, it's iconv.dll. And as of PHP 5.0.0, iconv is compiled into your Windows PHP binaries by default so no extra DLL is needed.